The present invention relates generally to medical devices, and more particularly to methods and apparatus for the endoluminal placement of tubular prostheses, such as grafts, for repairing aneurysms or other vascular defects in humans and animals.
Aneurysms are discrete dilations of the arterial wall, caused by weakening of the arterial wall. One of the most common, and among the most life threatening, is an aneurysm of the abdominal aorta between the renal and iliac arteries. If untreated, the aneurysm dilates progressively with an ever increasing risk of rupture and hemorrhagic death.
One method of treatment is provided by direct surgical intervention, in which the defective vessel may be bypassed or replaced using a prosthetic device such as a synthetic graft. The risks involved in direct surgical intervention of this magnitude are great, and include an extensive recovery period.
In recent years a less invasive method of treatment has evolved through a series of inventions. The details vary, but, conventionally, a resilient tubular conduit fashioned from flexible fabric (herein referred to as a “graft”) is introduced into the defective vessel by means of catheters introduced into the femoral artery. The graft is attached to the non-dilated or slightly dilated arteries above and below the aneurysm using expandable metallic cylinders (herein referred to as “attachment systems”) which may include barbs or hooks to enhance attachment to the vascular wall.
When an attachment system is positioned on the interior of a graft's lumen, it will tend to cause the outer wall of the graft to press against the inner wall of the vessel, thereby providing the additional function of providing a seal, preventing fluid flow to the region between the graft and the vascular wall.
However, the use of generally cylindrical grafts to reinforce vascular walls in a patient is not without problems. Grafts are required to be compressed into a catheter before being delivered and deployed into final position. Furthermore, grafts compressed into a catheter for delivery must be capable of bending around corners and branches of the patient's vascular system. The graft must accordingly be sufficiently flexible to satisfy these requirements.
One of the challenges encountered with the use of a flexible graft is that, because a diseased vessel is often irregularly shaped, the ends of the graft, even when urged outwardly by an attachment system, may not have a continuous circumferential edge pressed firmly against the inner wall of the vessel. As a result, fluid may leak into or out of (through a branch vessel) the region between the graft and the vascular wall, thereby increasing fluid pressure on the weakened walls of the vessel and reducing the protective effect of the graft. The same problem will occur if, as a result of an error in pre-operative sizing of the diseased vessel, a graft is provided that has a diameter slightly smaller than the diameter of the diseased vessel. Moreover, in the event the target vessel changes shape over time (i.e., increase in neck diameter or shrinkage in aneurysm), perigraft flow may occur. It will be appreciated that in these situations, because the fabric from which grafts are conventionally made is not circumferentially expandable, a complete seal around the circumference of the vessel will likely not be achieved.
Accordingly, there is a need for an improved graft that provides an enhanced seal for substantially preventing the flow of blood into the region between the graft and the vascular wall.